2020

Article

pf

icm

Symmetry breaking and the emergence of self-organized patterns is the hallmark of com-
plexity. Here, we demonstrate that a sessile drop, containing titania powder particles with
negligible self-propulsion, exhibits a transition to collective motion leading to self-organized
ﬂow patterns. This phenomenology emerges through a novel mechanism involving the
interplay between the chemical activity of the photocatalytic particles, which induces Mar-
angoni stresses at the liquid–liquid interface, and the geometrical conﬁnement provided by
the drop. The response of the interface to the chemical activity of the particles is the source
of a signiﬁcantly ampliﬁed hydrodynamic ﬂow within the drop, which moves the particles.
Furthermore, in ensembles of such active drops long-ranged ordering of the ﬂow patterns
within the drops is observed. We show that the ordering is dictated by a chemical com-
munication between drops, i.e., an alignment of the ﬂow patterns is induced by the gradients
of the chemicals emanating from the active particles, rather than by hydrodynamic
interactions.

Author(s):

Singh, D.P. and Domínguez, A. and Choudhury, U. and Kottapalli, S.N. and Popescu, M.N. and Dietrich, S. and Fischer, P.

Professor, University of Stuttgart<br/ >Max Planck Research Group Leader

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Our goal is to understand the principles of Perception, Action and Learning in autonomous systems that successfully interact with complex environments and to use this understanding to design future systems